Loud-speaking telephone



June 19, 1928.

- 1,674,539 I C. R. ALBERTUS noun SPEAKING TELEPnoriE Filed Aug'.,20, 1927 I/VVE/VTOE 0424 aze-5270s zms nv-roelvgx v Patented June 19, 1928.

UNITED STATES PATENT OFFICE.

CARL R, ALI BERTUS, OF SAN LEANDRO. CALIFORNIA, ASSIGNOB TO THE MAGNAVOX COMPANY, OF OAKLAND, CALIFORNIA, A CORPORATION OF ARIZONA.

LOUD-SPEAKIN G TELEPHONE.

My invention relates to mechanisms for driving telephone diaphragms and specifically to units of the balanced armature type.

An object of my invention is to provide a means whereby the space available for the coil winding can be used to greatest advantage.

A further object is to utilize a larger proportion of the flux from the permanent magnet than has hitherto been possible.

Another object is to produce a device in which a large amplitude of motion can be obtained without the use of cumbersome and ineflicient levers or linkages, and one which is simple and cheap to produce.

Referring to the drawings:

Figure 1 is a plan view of an embodiment of my device as it is usedto drive a conical diaphragm.

Figure 2 is an elevation of the same structure.

Figure 3 is a sectional view, the line 33 of Figure 1 indicating the plane of section.

Figure 4 is a detail of the pole piece and armature structure, with the coil removed for greater clarity.

Figure 5 is a diagrammatic view illustrating the angular relation of the air gaps.

Mechanisms of this general character consist of a permanent magnet and a pivoted armature held by spring action with its ends in the center of air gaps betweenpairs of pole pieces with which the magnet is provided.

. Surrounding the armature is a'coil which carries currents of the frequency ofthe sounds to be reproduced. These currents produce magnetic fluxes of the same frequency in the armature, and these fluxes cooperate with the flux from the permanent magnet to pull the armature from its central position in the air gaps against the action of the spring. A linkage connects the armature with a diaphragm,which communicates the vibrations to the air to produce sound.

In order that the mechanism may be most efiective, it is desirable that the armature be short, so that its magnetic'reluctance may have but little effect on the flux through it. This restricts the space allowablefor the col 1 It is also desirable that both air gaps be of the same length, and that the movement of the armature through the gaps be the same, for if one be short and the other lon an unequal flux distribution will result, wit a loss of efiiciency which may, in extreme cases, amount to a practical short circuiting of the flux.

It is desirable, too, to have the angle through which the armature vibrates small, as a rectilinear movement of the diaphragm is what is wanted. On the other hand, long lever arms are to be avoided as such are susceptible to parasitic vibrations which seriously impair the quality of reproduction. It will be seen that my mechanism combines these desirable elements in a high degree.

The earliest units of this type pivoted the armature in the center. tated dividing the coil in two to allow space for the pivoting structure. This resulted in Waste of coil space, and a relatively wide angular motion of the armature.

The next advance was to pivot the arma ture outside of the coil, and by reversing the pole pieces, i. e., by placing the north pole pieces at one end of the coil above the armature and at the other and below it, with a similar reversal of thesouth pole pieces, an operative device was produced. which used the available winding space more eflicient-ly and decreased thearc through which the armature moved. With this structure, however, either one air gap must be materially longer than the other; or the percentage of the gap through which the armature moves must be materially different at the two ends; or else the pivot about which the armature rotates must be so far removed from the driving portion of the mechanism as to make the'inter-related problems ofrigidity, weight, and parasitic vibration difficultof solution.

In the broad conception of my invention I pivot the arma-tureexternally to the coil and dispose the air gaps at different angles to the plane of movement of the armature, so that T am enabled to overcome all the difliculties which I have enumerated as atfecting this general type of structure.

In terms of greater detail, the present embodiment of my invention comprises a. per.- manent magnet 1 conveniently of horseshoe. type, and provided on one side adjacent the ends of its poles 2, 2 with a pole structure consisting of the blocks 3, 3; the rear pole pieces 4:, 4; and the front pole pieces 5, 5'.

This pole structure is secured to the poles of the magnet and to a brass base plate 6, by screws 7, 7'. The base plate is fixed on the outside face of the bottom wall 8 of the supporting housing or cage 9, a soft rubber pad 11 being interposed therebetwecn. The housing is mounted on the supporting structure 12 in which. the complete unit is embodied, by any suitable means disposed about the rim'13. v

The adjacent ends of the blocks 3, 3 are curved as best shown in Figure 4, to embrace the coil 14, suitably wound upon the hollow bobbin 16, held within the pole structure,

and extending thru an aperture formed for the purpose in the wall 8 ofthe housing. On the ligamentary spring 17, fixed at its ends to studs 18, extending from the plate 6 toward the magnet, is mounted the armature 19, extending from the vibrational axis thus established thru the bobbin and coil and lying within the air gaps 21 and 22 between the ends of the respective pairs of pole pieces.

it will be noted from an inspection of Figure 4 that the rear pole pieces 4. 4' areshaped to provide terminal surfaces defining the rear air gap 21 and that these surfaces lie in planes parallel to the vibrational axis of the spring 18, and at right angles to the plane of movement of the armature. The front pole pieces 5, 5' are also shaped to provide terminal surfaces defining the front air gap 22; and these surfaces lie in parallel planes forming an angle with the planes of the terminal surfaces of the rear pole pieces, and with the vibrational axis of the armature; and also with the plane of move ment of the armature. ranged so that these air gaps are of equal length. I

It will also be observed that the free end I 23 of the armatureis'twisted so that the end has-an angular relation to the main body of the armature equal to that between the two air gaps; or in other words, equal to the angular relation between the front air gap and the vibrational axis of the armature.

The armature is extended beyond the vibrational axisor fulcrum provided by the s ring 17 to form a. lever arm 24, adjacent e end'of which a pin or stud 26 is fixed. The stud "passes thru-an aperture in the housing wall 8 and is fixed to the cap 27,,

mounted on the point of the conical diaphragm secured at ts periphery to the annu ar leather flange'29, the outer edge of which is caught between the housing rim and an an-' nular clamp ring 31 secured-to the rimby screws 32. a

- In operation the'magnetiefiux provided by the p ermanent magnet divides, a portion passing through the rear pole plece 4, and

The parts are ar- 28,. lying within the, hou ing iid down through the air gap 21 to the pole piece 4. The remainder passes through the front pole piece 5 and up through the gap 22 to the pole piece 51. The-length of the air gaps being substantially the same, the

field strengths of the two are equal. It will be noted, however, that while the path of the magnetic fiuxin the rear gap 21 is in the direction of the plane of movement of the armature, the path of the magnetic flux in the frontgap'22 is at an angle 9 withthis plane of movement. It will also be notedthat the same angular value obtains between the two air gaps, and between the body and twisted end of the armature, each portion of which thus lies normal to the path of flux in its associated air gap.

When a current flows in the coil.14, it induces a flux in the armature with opposite poles at opposite ends of the coil. The fluxv from these poles co-operates with the flux from the pole pieces 4,4 and 5, 5', and since this flux also is in opposite directions at. oppositeends of the coil, thetotal effect is to urge the armature in one direction, which ivill be assumed to be down.

The armature now is not in the center of the gap, and since the reluctance of the armature is so low as compared with that of air as to be negligible, the larger portion of the flux from the magnet will pass through the pole piece 5, and the armature to the pole piece 4'. When the current in the coil is reversed the armature moves up wardly, and the larger partof the'permanent flux now flows from pole piece '4, through the armature to pole piece 5.

The distance from the vibrational axis of the armature to the rear pole piece may. be

is equal to the two gaps will change by the same amount, and maximum efi'ectiveness and minimum distortion in reproduction will result.

-A further eiiect of inclining the air gap to the plane of armature motion may, under some circumstances,'be highly desirable. In order. to radiate a large volume of'sound from a small diaphragm it is necessarythat it vibrate through a large amplitude. To

obtain this amplitude step -up'lev'erage systems have previously been employed, but it is difiicult to deslgn such systems with the tion in accordance with the principles above explained, the amplitude of armature motion may be increased so as to produce a result identical with that following the use of a longerlever arm.

I claim: i

1. A magnet. provided with pole pieces disposed in pairs to provide an air gap between each pair, the path of the magnetic flux in one air gap being at an angle to that in the other air gap.

2. A magnet PIOX'iClGd with pole pieces disposed in pairs to provide an air gap between each pair, the pa-th of the magnetic flux in one air gap being at an angle to that in the other air gap, and an armature mounted for movement in said air gaps.

3. A magnet provided with pole pieces disposed in pairs to provide an air gap between each pair, the path of the magnetic flux'in one air gap being at an angle to that in the other air gap, and an armature mounted for movement in said air gaps in a plane angular to the path of the magnetic flux in at least one of the air gaps.

4. A magnet provided with pole pieces disposed in pairs to provide an air gapbetween each pair, the path of the magnetic flux in one air gap being at an angle to that in the other air gap and an armature mounted for movement in said air gaps in' a plane angular to the path of the magnetic flux in one of the air gaps and parallel to the path of the magnetic flux in the other air gap. 4 e

5. A magnet provided with pole pieces disposed in pairs to provide an air gap between each pair, the path of the magnetic flux in one airgap being at an angle to that in the other air gap, and an armature pivotally mounted for movement in said air gaps.

6. A magnet provided with pole pieces disposed in pairs to provide an air gap between each pair, the path of the magnetic flux in one air gap being at. an angle to that in the other air gap, and an armature mounted for movement in said air gaps about an axis at one side thereof.

7. A magnet provided with pole pieces disposed in pairs to provide an air gap between each pair, the path of the magnetic flux in one air gap being at an angle to that in the other air gap, and an armature mounted for movement in said air gaps about an axis at one side thereof and parallel to the nearest air gap; the proportions conforming to the following formulae:

a='distance between axis and nearest air l b=clistance between axis and farthest air 9=angle between path of magnetic flux in the farthest. air gap and the plane of armature movement, and so chosen that cos 9=%- and a coil adapted to be energized disposedtabout said armature. I

9. A magnet provided wit-h pole pieces disposed in pairs to provide an air gap between each pair, the path of the magnetic flux in one air gap being at an angle to that in the other air gap, an armature mounted for movement in said air gaps, and a coil adapted to be energized disposed about said armature between the pairs of pole pieces.

10. In a sound reproducer, a permanent magnet provided with pole pieces disposed in spaced pairs and to provide an equal air gap between each pair, the path of the magnetic flux in one air gap being at an angle to that in the other air gap, an armature mounted for movement in said air gaps about an axis at one side thereof, a coil adapted to be energized disposed about said armature between the pairs of pole pieces, a diaphragm, and means connecting the armature to the diaphragm.

I 11. A magnet provided with pole pieces disposed in pairs to provide an air gap between each pair, the path of the magnetic flux in one air gap being at an angle tothat in the other air gap and the air gaps being substantially the same length.

. 12. A magnet provided with pole pieces disposed in pairs to provide an air gap between each pair, the path of the magnetic flux in one air gap being at an angle to that in theother air gap and the air gaps being substantially the same length, and an armature mounted for movement in said air gaps about an axis to one side thereof.

13. A magnet provided with pole pieces disposed inpairs to provide an air gap between each pair, the path of the magnetic flux in one air gap being at an angle to that in the other air gap and the air gaps being substantially the same length, and an armature mounted for movement in said air gaps about an axis to one side thereof, the proportions being such that the movement of the armature in both air gaps is relatively the same. 1

14. In a sound reproducer, a permanent magnet provided with pole pieces disposed in spaced pairs and to provide an equal air gap between each pair, the path of the mag netic flux in one air gap being at an angle to that in the other air gap, an armature mounted for movement in said air gaps about an axis at oneside thereof, a coil adapted to be energized disposed about said armature between the pairs of pole pieces, a diaphragm, and a lever arm fixed on the armature and operatively connected to said diaphragm.

15. In a sound reproducer a permanent magnet provided with pole pieces disposed in spaced pairs and to provide an equal air gap between each pair, the path of the magnetic flux in one air gap being at an angle 7 emme to that in the other air gap, an armature arranged in said air gaps, a mounting for said armature at one side of the pole piecesfor resiliently holding itin the center of the air gaps, a coil adapted to be energized disposed about said armature between the pole pieces, a diaphragm, and means connecting the armature to the diaphragm.

my hand.

' CARL R. ALBERTUS.

In testimony whereof, I have hereunto set 20 

